Epigallocatechin-3-O-gallate, the main green tea component, is toxic to Saccharomyces cerevisiae cells lacking the Fet3/Ftr1

Enantiomeric pairs of copper(II) complexes with tridentate Schiff bases derived from R- and S-methionine: the role of decorating organic groups of the ligand in crystal packing and biological activity

Three enantiomeric pairs consisting of copper(II) complexes with tridentate Schiff bases have been synthesized for employing in biological assessments: 1∞[Cu₂(R/S-salmet)₂(H₂O)] (1-R/S·H2O), 1∞[Cu(R/S-3-HOMe-5-Me-salmet)] (2-R/S), and 1∞[Cu(R/S-3-MeO-salmet)] (3-R/S) (where R/S-salmetH₂, R/S-3-HOMe-5-Me-salmetH₂, and R/S-3-MeO-salmetH₂ result from the condensation of R/S-methionine with salicylaldehyde, 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde, and 3-methoxy-salicylaldehyde, respectively, in a 1 : 1 molar ratio). The crystal structures of 1-R·H2O and 2-R/S are reported. Moreover, the 1-R/S·H2O enantiomers have been subjected to a single-crystal-to-single-crystal (SC-SC) transformation by heating at 160 °C to afford their dehydrated forms, 1∞[Cu₂(R/S-salmet)₂] (1-R/S), whose structures have also been crystallographically determined. The coordination polyhedra of the metal centers, the binding modes of the ligands, and the 1-D double chain assemblies generated by the chiral mononuclear units are comparatively described. The diffuse reflectance UV-Vis and circular dichroism (CD) spectra of compounds 1-R/S·H2O, 1-R/S, and 2-R/S are analysed with respect to their structural peculiarities and compared to those of 3-R/S. The UV-Vis and CD spectra of solutions of 1-R/S, 2-R/S, and 3-R/S point to the collapse of the double chains via dissolution. Biological tests performed on the model eukaryote Saccharomyces cerevisiae indicated low toxicity for 1-R/S, 2-R/S, and 3-R, and moderate toxicity for 3-S. The S-type complexes were accumulated by cells in higher quantity compared to their R-type counterparts due to selective transport via the high-affinity S-methionine transporter, Mup1. A chemogenomic analysis of 3-S toxicity performed on a collection of yeast knockout mutants revealed that most of the deleted genes identified in the screen were involved in the cell response to oxidative stress, calcium-mediated response, or metal homeostasis. Altogether, it was concluded that 3-S accumulation may perturb the redox state of the cell, also interfering with the calcium-mediated response to oxidative stress or metal-related oxidative stress.

Saccharomyces cerevisiae Concentrates Subtoxic Copper onto Cell Wall from Solid Media Containing Reducing Sugars as Carbon Source

Copper is essential for life, but it can be deleterious in concentrations that surpass the physiological limits. Copper pollution is related to widespread human activities, such as viticulture and wine production. To unravel aspects of how organisms cope with copper insults, we used Saccharomyces cerevisiae as a model for adaptation to high but subtoxic concentrations of copper. We found that S. cerevisiae cells could tolerate high copper concentration by forming deposits on the cell wall and that the copper-containing deposits accumulated predominantly when cells were grown statically on media prepared with reducing sugars (glucose, galactose) as sole carbon source, but not on media containing nonreducing carbon sources, such as glycerol or lactate. Exposing cells to copper in liquid media under strong agitation prevented the formation of copper-containing deposits at the cell wall. Disruption of low-affinity copper intake through the plasma membrane increased the potential of the cell to form copper deposits on the cell surface. These results imply that biotechnology problems caused by high copper concentration can be tackled by selecting yeast strains and conditions to allow the removal of excess copper from various contaminated sites in the forms of solid deposits which do not penetrate the cell.

Saccharomyces cerevisiae cells lacking transcription factors Skn7 or Yap1 exhibit different susceptibility to cyanidin

Anthocyanidins – the aglycone moiety of anthocyanins – are responsible for the antioxidant traits and for many of the health benefits brought by the consumption of anthocyanin-rich foods, but whether excessive anthocyanidins are deleterious to living organisms is still a matter of debate. In the present study we used the model eukaryotic microorganism Saccharomyces cerevisiae to evaluate the potential toxicity of cyanidin, one of the most prevalent anthocyanidins found in berries, grapes, purple vegetables, and red wine. We found that yeast cells lacking the transcription factors responsible for regulating the response to oxidative stress – Skn7 and Yap1 – exhibited different sensitivities to cyanidin. Cells lacking the transcription factor Skn7 were sensitive to low concentrations of cyanidin, a trait that was augmented by exposure to visible light, notably blue or green light. In contrast, the growth of yeast cells devoid of Yap1 was stimulated by low concentrations, but it was impaired by high cyanidin exposure. High, but not low cyanidin was shown to induce Yap1 translocation from cytosol to nucleus, probably by generating reactive oxygen species such as H₂O₂. Taken together, these observation suggested that Skn7 and Yap1 have complementary roles in adaptation to cyanidin stress, with Skn7 involved in adaptation to low concentrations and with Yap1 responsible for adaptation to high concentrations of cyanidin. The results imply that caution is needed when utilizing cyanidin-enriched supplements, especially when in combination with prolonged exposure to visible light.

Interaction between Polyphenolic Antioxidants and Saccharomyces cerevisiae Cells Defective in Heavy Metal Transport across the Plasma Membrane

Natural polyphenols are compounds with important biological implications which include antioxidant and metal-chelating characteristics relevant for their antimicrobial, antitumor, or antiaging potential. The mechanisms linking polyphenols and heavy metals in their concerted actions on cells are not completely elucidated. In this study, we used the model eukaryotic microorganism Saccharomyces cerevisiae to detect the action of widely prevalent natural polyphenols on yeast cells defective in the main components involved in essential heavy metal transport across the plasma membrane. We found that caffeic and gallic acids interfered with Zn accumulation, causing delays in cell growth that were alleviated by Zn supplementation. The flavones morin and quercetin interfered with both Mn and Zn accumulation, which resulted in growth improvement, but supplemental Mn and especially Zn turned the initially benefic action of morin and quercetin into potential toxicity. Our results imply that caution is needed when administering food supplements or nutraceuticals which contain both natural polyphenols and essential elements, especially zinc.